Multi-layered fire door and method for making the same

ABSTRACT

A door has a core that includes a porous layer having a thickness and two opposing major surfaces. In one construction, the core also includes three fire-retardant layers, and two of the fire-retardant layers are separated by the porous layer. The porous layer and the fire-retardant layers are coupled together. Other constructions include one or more fire-retardant layers in balanced or unbalanced placement around the porous layer.

NOTICE OF COPYRIGHT PROTECTION

A portion of the disclosure of this patent document and its figurescontain material subject to copyright protection. The copyright ownerhas no objection to the facsimile reproduction by anyone of the patentdocument, but otherwise reserves all copyrights whatsoever.

FIELD OF THE INVENTION

This invention relates to doors in general, and more particularly to afire door having several fire-retardant layers.

BACKGROUND

Fire doors are designed and installed in an attempt to protect lives andproperty from fire, smoke, and heat by providing a barrier to withstandthe fire, smoke, and heat for a period of time. To be labeled orcertified as a fire door, a door must fulfill the requirements ofcertain codes or standards that regulate the construction andinstallation of such doors. These codes or standards include, amongothers, the Uniform Building Code (UBC), and codes promulgated by theNational Fire Protection Association (NFPA), and American Society forTesting and Materials (ASTM).

Private testing laboratories, such as Underwriters' Laboratories andWarnock Hersey, may test for adherence to such codes or standards, andmay test for additional attributes. The laboratories may also certifythat a fire door meets fire protection requirements after conductingtesting (such as destructive testing) of the door. Usually, thiscertification is expressed as a fire-rating offering a specific level ofprotection from fire, smoke, and/or heat for a limited amount of time.For example, a 20-minute fire-rated door should, if installed correctly,maintain its structural integrity and provide a barrier to fire, heat,and/or smoke for at least 20 minutes. So long as a door meets relevantfire protection requirements, its design may vary to fulfill otherdesign considerations, such as weight, cost of manufacture, andaesthetic appearance.

An interior routed medium-density fiberboard (MDF) fire door meetingcurrent fire protection requirements generally is constructed of aone-and-one-half inch thick sheet of MDF having a minimum density ofapproximately 42 pounds per cubic foot (pcf) and a one-eighth of an inchhardboard skin on both sides of the MDF. A single-swing wood fire doorusing MDF having this thickness and density, and that is three feet wideby eight feet high, weighs nearly 153 pounds. Not only is such a doorextremely heavy, but manufacturing it can be costly and difficult aswell.

For example, manufacturing a molded-panel fire door that meets currentfire protection requirements generally requires using a mold. There areseveral ways known to prepare molds. One common method is to usematching castings or dies. A molded door generally has two exteriorskins, and one mold is required for each skin. To make a custom-ordereddoor, a new mold must be created. While using molds to make a paneleddoor is generally less costly on a high-volume basis than machiningreliefs into a door, molding custom-ordered doors can significantly addto the manufacturing expense—in some cases, this expense can becomecost-prohibitive.

Manufacturing paneled wood doors without molds is known in the art. Suchdoors generally include two exterior skins with a core inserted betweenthe skins. In one such conventional door, the core generally includes athree-eights-of-an-inch-thick layer of MDF, athree-eights-of-an-inch-thick layer of expanded polystyrene, and anotherthree-eights-of-an-inch-thick layer of MDF. The layers of the core areadhered to one another, as are the external skins and the core. Woodside stiles and top and bottom rails are then adhered to an outerperimeter of the door. Panels are formed by routing a series of groovesinto the external skins.

SUMMARY OF THE INVENTION

The present invention includes multi-layered fire doors and methods formaking such doors. One embodiment of the present invention provides afire door that includes a core. The core has a porous layer having athickness and two opposing major surfaces. The core also has at leastthree, preferably fire-retardant, additional layers. Each of the threefire-retardant layers has a thickness and two opposing major surfaces.The porous layer and the at least three fire-retardant layers arecoupled together. At least two of the at least three fire-retardantlayers are separated by the porous layer from the other fire-retardantlayers. The fire door can also include first and second exterior layers,each having a thickness and two opposed major surfaces. A grooved firstpattern can be disposed on the first exterior layer and a grooved secondpattern can be disposed on the second exterior layer.

The fire-retardant layers may be made of any suitable material. In oneembodiment, the fire-retardant layers are made of MDF having a densityof at least 42 pcf. Likewise, the porous layer can be made of anysuitable material. One example is a thermoplastic polymer having adensity of at least 1 pcf. The thickness of each of the fire-retardantlayers is the same. The thickness of the porous layer is approximatelythe same as the thickness of each fire-retardant layer. The first andsecond exterior layers can include a hardboard having a density ofapproximately 52 pcf. The thicknesses of the first and second exteriorlayers are approximately the same.

Another embodiment of the present invention provides a fire door thatincludes a core with a porous layer having a thickness of approximatelythree-eighths of an inch and two opposing major surfaces. The core alsohas at least two, preferably fire-retardant, additional layers. Each ofthe two fire-retardant layers has a thickness of approximatelynine-sixteenths of an inch and two opposing major surfaces. The porouslayer and the at least two fire retardant layers are coupled together.The at least two fire-retardant layers are separated by the porouslayer.

An embodiment of the present invention further provides for methods ofmaking a door having a core with a porous layer and two opposing majorsurfaces and fire-retardant layers, each having a thickness and twoopposing major surfaces. One embodiment of a method according to thepresent invention includes coupling together a porous layer and at leastthree fire-retardant layers. At least two of the fire-retardant layersare separated by the porous layer. The door can also include first andsecond exterior layers each having a thickness and two opposed majorsurfaces. In one embodiment, the method according to the presentinvention also includes forming a blank by coupling the first and secondexterior layers to the core. An embodiment further includes applying agenerally uniform pressure to the blank for a period of time. A furtherembodiment includes machining a grooved first pattern on the firstexterior surface and machining a grooved second pattern on the secondexterior surface.

An advantage of one embodiment of the present invention is to provide afire-rated door that can endure a 20-minute fire test according to atleast the following standards: UBC 7-2 (1997), Part I NFPA 252 (1999),UL 10C (1998), ASTM E 2072 (1999), and CAN4 S113 and WH-PN-014 (1985).

Another advantage of one embodiment of the present invention is toprovide a lighter-weight fire-rated door, i.e., approximately 120 pounds(having dimensions of three feet by eight feet by one-and-three-quartersof an inch), than is currently available.

Yet another advantage of one embodiment of the present invention is toreduce the complexity and cost of manufacturing wood, paneled fire-rateddoors by forming panels in the door by machining, instead of molding.

A further advantage of one embodiment of the present invention is toincrease a fire door manufacturer's flexibility in manufacturingcustomer-ordered wood, paneled fire-rated doors by forming panels in thedoor by machining, rather than by molding.

Yet a further advantage of one embodiment of the present invention is toimprove the insulative qualities, or R-value, of fire-rated doors.

An additional advantage of one embodiment of the present invention is toimprove the sound dampening of fire-rated doors.

Yet another additional advantage of one embodiment of the presentinvention is to reduce a fire-rated door's susceptibility to warpingcaused by moisture.

Additional advantages of embodiments of the invention are set forth inthe detailed description that follows and will become more apparent tothose skilled in the art upon examination of the following.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, help to illustrate embodiments of theinvention. In the drawings, like numerals are used to indicate likeelements throughout.

FIG. 1 is a front plan view of a double door system according to anembodiment of the invention.

FIG. 2 is a partially-exploded orthogonal view of the door of FIG. 1prior to machining panels.

FIG. 3 is a flow diagram of a method of making the door of FIG. 1.

FIG. 4 is a flow diagram of a method of making a door blank of FIG. 1.

FIG. 5 is a front plan view of a door according to another embodiment ofthe invention.

FIG. 6 is a partially-exploded orthogonal view of the door of FIG. 5.

DETAILED DESCRIPTION

The present invention includes doors, parts of doors, and methods ofmaking doors. One embodiment of the present invention includes amultilayer fire door and methods of making such a door.

FIG. 1 shows a front plan view of a door according to an embodiment ofthe invention. A standard-pair wood, paneled fire door 100 includes twoseparate but adjacent doors, 110 and 210. The door 100 can also be asingle-swing door (not shown). As doors 110 and 210 are identical inmaterial respect, only door 110 will be described in detail.

Door 110 has a major axis and a minor axis. The major axis extendsvertically and the minor axis extends horizontally. The door 110includes an outer peripheral frame including a bottom rail 112, a toprail 114, and a pair of side stiles 116 and 118. The top rail 114 andthe bottom rail 112 extend horizontally along the minor axis andgenerally parallel to one another. The side stiles 116 and 118 extendvertically along the major axis and generally parallel to one another.The top rail 114 and the bottom rail 112 are generally perpendicular tothe side stiles 116 and 118. The top rail 114 and the bottom rail 112are made of MDF having a density of at least 42 pcf. The side stiles 116and 118 are made of pine or fir, preferably, having a minimum specificgravity of 0.34. The side stiles 116 and 118 can be made of another typeor kind of wood. Preferably, the specific gravity of that wood is aminimum of 0.34. Moreover, the rails 112 and 114, and the stiles 116 and118 may be made of any suitable material.

The door 110 also includes hinges 120 to mount the door 110 to a hingejamb 410 to allow the door 110 to swing open and closed. As shown inFIG. 1, there are four hinges 120 mounting the door 110 to the hingejamb 124. The number of hinges 120 can vary to accommodate variousdesign considerations, such as the weight of the door 110. A handle 122is provided on the door 110 to operate a latch (not shown), whichmaintains the door 110 in a closed position. While door 210 can beopened and closed, the door 210 preferably is maintained in a closedposition. The latch on door 110 maintains the door 110 in a closedposition by engaging with a complementary recess (not shown) on door210. A width and a height of the doors 110 and 210 can vary but, ingeneral, should not exceed approximately three feet in width and eightfeet in height.

In general, the above description of the door's features visible in FIG.1 comprise conventional door construction. It is included here forcompleteness, and to aid one of ordinary skill in the art inconstructing a door according to the present invention.

Referring now to FIG. 2, the door 110 includes a core 130, which isdisposed between a front face 140 and a rear face 190. The core 130shown has several layers of material. The layers 150, 160, 170, 180 maybe made of any suitable material. Preferably, at least three of thelayers 150, 160, 180 are made of fire-retardant material. Preferably,the layers of fire-retardant material comprises MDF. Most preferably,the layers comprise MDF having a density of approximately 42 pcf. Thecore 130 includes a first fiberboard 150, a second fiberboard 160, and athird fiberboard 180. Disposed between the second and third fiberboards160 and 180 is a layer of porous material 170. The porous layer 170 maybe made of any suitable material. Preferably, the porous layer 170 is afoam sheet comprised of a thermoplastic polymer, such as expandedpolystyrene, having a density of at least 1 pcf. Alternatively, theporous layer 170 can be a fire-retardant material.

Each of the front face 140, the rear face 190, the first fiberboard 150,the second fiberboard 160, the third fiberboard 180, and the porouslayer 170 has two major surfaces and a thickness. A height and width ofeach of the front face 140, the rear face 190, the first fiberboard 150,the second fiberboard 160, the third fiberboard 180, and the porouslayer 170 correspond generally to the height and width of the door 110.

An exemplary embodiment of such a door 110 comprises each of the frontface 140, the rear face 190, the first fiberboard 150, the secondfiberboard 160, the porous layer 170, and the third fiberboard 180having dimensions of three feet wide by eight feet high. This exemplaryembodiment also comprises the thickness of both the front face 140 andthe rear face 190 being one-eighth-of-an-inch. In this exemplaryembodiment the thickness of each of the first fiberboard 150, the secondfiberboard 160, the porous layer 170, and the third fiberboard 180 isthree-eighths-of-an-inch. Alternatively, any other suitable dimensionscan be provided.

The front face 140 and the rear face 190 may be made of any suitablematerial. Preferably, the front face 140 and the rear face 190 are ahardboard made of wood fibers having a density of at least 52 pcf. Thehardboard of the front face 140 and the rear face 190 can be made of anyother suitable material, preferably, having a density of at least 52pcf. The thicknesses of the front face 140 and the rear face 190 showncan be the same. The thickness of the front face 140 shown is one-eighthof an inch, as is the thickness of the rear face 190. Alternatively,these thicknesses can be approximately one-eighth of an inch or anyother suitable thickness. The two major surfaces of the front face 140include a front-facing surface 141 and a rear-facing surface (notshown). The front-facing surface 141 and the rear-facing surface of thefront face 140 are disposed on opposing sides of the front face 140.Either the front-facing surface 141 or the rear-facing surface of thefront face 140 can be disposed adjacent to one of the major surfaces ofthe first fiberboard 150. In the embodiment shown in FIG. 2, therear-facing surface of the front face 140 is disposed adjacent to thefirst fiberboard 150.

The first fiberboard 150 can be formed by disposing a vertical splice152 adjacent to a main sheet 154. Alternatively, the first fiberboard150 can be a single sheet. The vertical splice 152 can be disposedproximate the side stile 116. The width of the vertical splice 152 canbe any suitable dimension. For example, the width of the vertical splice152 can be six inches. The width of both the vertical splice 152 and themain sheet 154 correspond generally to the width of the door 110. Thus,the maximum dimensions of the fiberboard 150 are three feet wide byeight feet high. The height of the vertical splice 152 is preferably thesame as the height of the main sheet 154. Preferably, the dimensions ofthe side stiles 116 and 118 are one-and-one-quarter inches byone-and-one-half inches. Preferably, the dimensions of the bottom rail112 and the top rail 114 is one-and-one-quarter inches byone-and-one-half inches by thirty-three-and-seven-eighths inches.Alternatively, any other suitable dimensions can be used.

The thickness of the first fiberboard 150 shown is three-eighths of aninch. Alternatively, the thickness can be approximately three-eights ofan inch or any other suitable thickness. The two major surfaces of thefirst fiberboard 150 include a front-facing surface 151 and arear-facing surface (not shown). The front-facing surface 151 and therear-facing surface of the first fiberboard 150 are disposed on opposingsides of the first fiberboard 150. Either the front-facing surface 151or the rear-facing surface of the first fiberboard 150 can be disposedadjacent to the rear-facing surface of the front face 140. According tothe embodiment, the front-facing surface 151 of the first fiberboard 150is disposed adjacent to the rear-facing surface of the front face 140.Thus, the rear-facing surface of the first fiberboard 150 is disposedadjacent to one of the major surfaces of the second fiberboard 160.

The second fiberboard 160 is formed by disposing a vertical 162 spliceadjacent to a main sheet 164. Alternatively, the second fiberboard 160can be a single sheet. The vertical splice 162 is disposed proximate theside stile 118. The width of the vertical splice 162 can be any suitabledimension. For example, the width of the vertical splice can be sixinches. The width of both the vertical splice 162 and the main sheet 164corresponds to the width of the door 110. Thus, the maximum dimensionsof the fiberboard 160 are three feet wide by eight feet high. The heightof the vertical splice 162 is the same as the height of the main sheet164.

The thickness of the second fiberboard 160 is preferably three-eighthsof an inch. It can be approximately three-eighths of an inch or another,selected thickness. The two major surfaces of the second fiberboard 160include a front-facing surface 161 and a rear-facing surface (notshown). The front-facing surface 161 and the rear-facing surface of thesecond fiberboard 160 can be disposed on opposing sides of the secondfiberboard 160. Either the front-facing surface 161 or the rear-facingsurface of the second fiberboard 160 can be disposed adjacent to therear-facing surface of the first fiberboard 150. According to theembodiment, the front-facing surface 161 of the second fiberboard 160 isdisposed adjacent to the rear-facing surface of the first fiberboard150. Thus, the rear-facing surface of the second fiberboard 160 isdisposed adjacent to one of the major surfaces of the porous layer 170.

Preferably, the porous layer 170 is formed by disposing a horizontalsplice 172 adjacent to a main sheet 174. Alternatively, the porous layer170 can be a single sheet. The horizontal splice 172 is disposedproximate the top rail 114. Alternatively, the horizontal splice 172 isdisposed proximate the bottom rail 112. The dimension of the horizontalsplice 172 can be any suitable dimension. For example, the height of thesplice 172 can be 16 inches. The height of both the horizontal splice172 and the main sheet 174 correspond to the height of the door 110.Thus, the maximum dimensions of the porous layer 170 are three feet wideby eight feet high. The width of the horizontal splice 172 is the sameas the width of the main sheet 174. The thickness of the porous layer170 shown is three-eighths of an inch. In another embodiment, it isapproximately three-eighths of an inch or another thickness.

The two major surfaces of the porous layer 170 include a front-facingsurface 171 and a rear-facing surface (not shown). The front-facingsurface 171 and the rear-facing surface of the porous layer 170 aredisposed on opposing sides of the porous layer 170. Either thefront-facing surface 171 or the rear-facing surface of the porous layer170 can be disposed adjacent to the rear-facing surface of the secondfiberboard 160. According to the embodiment, the front-facing surface171 of the porous layer 170 is disposed adjacent to the secondfiberboard 160. Thus, the rear-facing surface of the porous layer 170 isdisposed adjacent to one of the major surfaces of the third fiberboard180.

The third fiberboard 180 is formed by disposing a vertical splice 182adjacent to a main sheet 184. Alternatively, the third fiberboard 180can be a single sheet. The vertical splice 182 is disposed proximate theside stile 116. Alternatively, the vertical splice 182 can be disposedproximate the side stile 114. The width of the vertical splice 182 canbe any suitable dimension. For example, the width of the vertical splice182 can be approximately six inches. Preferably, the width of both thevertical splice 182 and the main sheet 184 corresponds to the width ofthe door 110. Thus, the maximum dimensions of the third fiberboard 180are three feet wide by eight feet high. The height of the verticalsplice 182 is the same as the height of the main sheet 184.

The thickness of the third fiberboard 180 is preferably three-eighths ofan inch. Alternatively, the thickness can be approximately three-eightsof an inch or another suitable thickness. The two major surfaces of thethird fiberboard 180 include a front-facing surface 181 and arear-facing surface (not shown). The front-facing surface 181 and therear-facing surface of the third fiberboard 180 are disposed on opposingsides of the third fiberboard 180. Either the front-facing surface 181or the rear facing surface of the third fiberboard 180 can be disposedadjacent to the rear-facing surface of the porous layer 170. Accordingto the embodiment described herein, the front-facing surface 181 of thethird fiberboard 180 is disposed adjacent to the rear-facing surface ofthe porous layer 170. Thus, the rear-facing surface of the thirdfiberboard is disposed adjacent to one of the major surfaces of the rearface 190.

As described above, the rear face 190 includes a hardboard preferablyhaving a density of at least 52 pcf and the thickness is one-eighth ofan inch. Alternatively, the thickness can be approximately one-eighth ofan inch or another suitable thickness. The two major surfaces of therear face 190 include a front-facing surface 191 and a rear-facingsurface (not shown). The front-facing surface 191 and the rear-facingsurface of the rear face 190 are disposed on opposing sides of the rearface 190. Either the front-facing surface 191 or the rear-facing surfaceof the rear face 190 can be disposed adjacent to the rear-facing surfaceof the third fiberboard 180. According to the embodiment, thefront-facing surface 191 of the rear face 190 is disposed adjacent tothe rear-facing surface of the third fiberboard 180.

To enhance the aesthetic appearance of the door 110, a series of grooves142 are disposed in the front face 140 of the door 110 forming panels144. Alternatively, the door 110 can be flush and have no panels. Asshown in FIG. 1, one embodiment preferably includes twelve panels 144formed in the front face 140 of the door 110. The number and shape ofthe panels 144 can vary depending on the design desired. As will bedescribed in more detail below, the grooves 142 are formed by machining,such as routing, into the door 110. In the embodiment, the depth of thegrooves 142 preferably are seven-sixteenths of an inch. Thus, thegrooves 142 penetrate the entire thicknesses of the front face 140 andnearly the entire thickness of the first fiberboard 150. Although notshown, panels are preferably formed in the rear face 190. In general,the depth of the grooves in the panels formed in the rear face 190preferably are the same as that of the front face 140, butalternatively, can be different than that of the front face. Thus, thegrooves in the rear face 190 penetrate the entire thickness of the rearface 190 and nearly the entire thickness of the third fiberboard 180.

As described above, a conventional door made entirely of MDF weighsapproximately 153 pounds. The weight of the door 110 according to theembodiment as described above is substantially less. Using a similarlydimensioned door, i.e., three feet wide and eight feet high, with thethicknesses described above, the door 110 according to the embodimentshould weigh approximately 120 pounds. The weight of the door 110 isreduced further by the weight of the material removed by machining thegrooves to form the panels in the door 110.

A method of making the door 110 according to an embodiment will bedescribed next with reference to FIG. 3. As described above, the core130 includes the first fiberboard 150, the second fiberboard 160, thethird fiberboard 180, and the porous layer 170. The method includescoupling together the porous layer 170 and the first fiberboard 150, thesecond fiberboard 160, and the third fiberboard 180. Preferably,coupling refers to joining by adhering surfaces together with anadhesive, such as glue or cement, as described below. A variety ofcommercially-available adhesives can be used, including, for example,Tightbond® 100 manufactured by Franklin International, RK-3490manufactured by H.B. Fuller Co., and WD-1300C0-2F manufactured bySpecialty Polymers, Inc. Other suitable methods of joining surfacestogether can be used.

In the embodiment shown in FIG. 2, two of the first fiberboard 150, thesecond fiberboard 160, and the third fiberboard 180 are separated by theporous layer 170. An embodiment of the method of making the core 130 ofthe door 110 is described in further detail below and in FIG. 4.

FIG. 3 is a flow chart diagram illustrating a method of making the door110. A door blank (not shown) is first assembled as indicated by block310. The rear face 190 can be placed on a flat surface, such as a lay-uptable (not shown). Either the front-facing surface 191 or therear-facing surface of the rear face 190 can be placed on the flatsurface. According to the embodiment, the rear-facing surface of therear face 190 is placed on the flat surface.

Preferably, an adhesive (not shown) is applied to at least one surfaceof each of the side stiles 116 and 118 and the bottom rail 112 and thetop rail 114. As indicated by block 311 in FIG. 4, the side stiles 116and 118 and the bottom rail 112 and the top rail 114 are attached, inpositions corresponding to those shown in FIG. 2, on the door blank asthus far constructed.

Preferably, the adhesive is applied to both the front-facing surface 181and the rear-facing surface of the third fiberboard 180. Alternatively,the adhesive can be applied to either the front-facing surface 181 orthe rear-facing surface of the third fiberboard 180. As indicated byblock 312 in FIG. 4, either the front-facing surface 181 or therear-facing surface of the third fiberboard 180 can be placed on therear face 190. Preferably, the rear-facing surface of the thirdfiberboard 180 is placed on and adhered to the front-facing surface 191of the rear face 190.

Preferably, the adhesive is applied to both the front-facing surface 171and the rear-facing surface of the porous layer 170. Alternatively, theporous layer 170 can be placed on the third fiberboard 180 with noadhesive applied to the porous layer 170. Alternatively, the adhesivecan be applied to either the front-facing surface 171 or the rear-facingsurface of the porous layer 170. As indicated by block 313 in FIG. 4,either the front-facing surface 171 or the rear-facing surface of theporous layer 170 can be placed on the third fiberboard 180. Preferably,the rear-facing surface of the porous layer 170 is placed on thefront-facing surface 181 of the third fiberboard 180.

Preferably, the adhesive is applied to both the front-facing surface 161and the rear-facing surface of the second fiberboard 160. Alternatively,the adhesive can be applied to either the front-facing surface 161 orthe rear-facing surface of the second fiberboard 160. As indicated byblock 314 in FIG. 4, either the front-facing surface 161 or therear-facing surface of the second fiberboard 160 can be placed on theporous layer 170. Preferably, the rear-facing surface of the secondfiberboard 160 preferably is placed on the front-facing surface 171 ofthe porous layer 170.

Preferably, the adhesive is applied to both the front-facing surface 151and the rear-facing surface of the first fiberboard 150. Alternatively,the adhesive can be applied to either the front-facing surface 151 orthe rear-facing surface of the first fiberboard 150. As indicated byblock 315 in FIG. 4, either the front-facing surface 151 or therear-facing surface of the first fiberboard 150 can be placed on thesecond fiberboard 160. Preferably, the rear-facing surface of the firstfiberboard 150 is placed on and adhered to the front-facing surface 161of the second fiberboard 161.

As indicated by block 316 in FIG. 4, either the front-facing surface 141or the rear-facing surface of the front face 140 can be placed on thefirst fiberboard 150. Preferably, the rear-facing surface of the frontface 140 is placed on the front-facing surface 151 of the firstfiberboard 150. The door blank of the embodiment has thus beenconstructed.

As indicated by block 320 in FIG. 3, pressure is applied to the doorblank. Preferably, several door blanks are placed one atop the other andplaced in a press (not shown) at the same time. Alternatively, only onedoor is placed in the press. A pressure in a range between 80 and 110pounds per square inch (psi) is applied to the door blank for 30minutes. Alternatively, the pressure can be in a range betweenapproximately 80 psi and approximately 110 psi. Alternatively, the timethe pressure is applied can be approximately 30 minutes. Alternatively,any other suitable pressure and time can be used. In general, press timewill be longer when the ambient temperature is below 65 degrees F. Thepressure is removed from the door blank and the adhesive is allowed toadhere for at least approximately eight hours. During this time, thedoor blank is not manipulated. As indicated by block 330 in FIG. 3, thedoor blank is cut to a desired width and height. Preferably, the maximumwidth does not exceed three feet and the maximum height does not exceedeight feet.

As indicated by block 340, a series of grooves 142 are machined into thefront face 140 to form the panels 144. Alternatively, the front face 140can be flush with no panels. Once the panels 144 have been formed, theblank is turned over so that another series of grooves are machined intothe rear face 190 to form other panels. The machining is preferablyaccomplished by routing. Generally, a computer program is written tocontrol a computer numerical control (CNC) milling machine (not shown).The door blank is placed into the milling machine and one side of thedoor blank is milled according to the design entered into the CNCmilling machine. Hardware, such as the door handle 122 is installed. Thedoor 110 can thus be installed into a door frame 132.

Other variations to the embodiments described above are possible. Forexample, the thickness of any of the layers forming the door can bevaried from that described above. Similarly, varying the density of thelayers forming the door in the above embodiments is certainly within theordinary skill in the art.

The embodiments shown in FIG. 2 are an unbalanced core construction;that is, in the embodiments shown in FIG. 2, the number offire-retardant layers on one side of the porous layer is not equal tothe number of fire-retardant layers on the other side of the porouslayer. Specifically, the embodiments shown in FIG. 2 include onefire-retardant layer on one side of the porous layer and twofire-retardant layers on the other side of the porous layer. The numberof layers on each side of the porous layer can be varied in otherembodiments. For example, there can be two layers on one side of theporous layer and three layers on the other side. As another example,there can be an equal number of layers on each side of the porous layerbut the thickness of the fire-retardant layers on one side of the porouslayer is different than the thickness of the fire-retardant layers onthe other side.

Furthermore, a core of the door in accordance with the present inventioncan have a balanced construction. In order words, a balanced coreconstruction has an equal number of layers on each side of the porouslayer. For example, there can be one fire-retardant layer on each sideof the porous layer. There can be more than one fire-retardant layer oneach side of the porous layer. Moreover, in the balanced construction,the total thickness of fire-retardant layers on one side of the porouslayer can be the same as the total thickness of fire-retardant layers onthe other side of the porous layer even if the number of layers on eachside differs. An example of an embodiment disclosing a balancedconstruction will be described below.

FIG. 5 shows a front plan view of a door according to another embodimentof the invention. A standard-pair wood, paneled fire door 400 includestwo separate but adjacent doors, 410 and 510. The door 400 can also be asingle-swing door (not shown). As the external appearance of door 400and door 100 are identical in material respect—including the grooves andpanels, these identical details will not be repeated. Thus, only thecore 430 will be described in detail below. Furthermore, as doors 410and 510 are identical in material respect, only door 410 will bedescribed in detail.

Referring now to FIG. 6, the door 410 includes a core 430, which isdisposed between a front face 440 and a rear face 490. The core 430shown has several layers of material. The layers 450, 470, and 480 maybe made of any suitable material. Preferably, at least two of the layers450 and 480 are made of fire-retardant material. Preferably, the layersof fire-retardant material comprise an MDF. Most preferably, the layerscomprise MDF having a density of approximately 42 pcf. The core 430includes a first fiberboard 450 and a second fiberboard 480. Disposedbetween the first and second fiberboards 450 and 480 is a layer ofporous material 470. The porous layer 470 may be made of any suitablematerial. Preferably, the porous layer 470 is a foam pad comprised of athermoplastic polymer, such as expanded polystyrene, having a density ofat least 1 pcf.

Each of the first fiberboard 450, the second fiberboard 480, and theporous layer 470 has two major surfaces and a thickness. A height andwidth of each of the first fiberboard 450, the second fiberboard 480,and the porous layer 470 correspond generally to the height and width ofthe door 410.

An exemplary embodiment of a core 430 of such a door 410 comprises eachof the first fiberboard 450, the second fiberboard 480, and the porouslayer 470 having dimensions of three feet wide by eight feet high. Inthis exemplary embodiment the thickness of each of the first fiberboard450 and the second fiberboard 480 is nine-sixteenths-of-an-inch and thethickness of the porous layer 470 is three-eighths-of-an-inch.Alternatively, any other suitable dimensions can be provided.

In the embodiment shown in FIG. 6, the first fiberboard 450 can beformed by disposing a vertical splice 452 adjacent to a main sheet 454.Alternatively, the first fiberboard 450 can be a single sheet. Thevertical splice 452 is preferably disposed proximate the side stile 416.The width of the vertical splice 452 can be any suitable dimension. Forexample, the width of the vertical splice can be six inches. The widthof both the vertical splice 452 and the main sheet 454 correspondgenerally to the width of the door 410. Thus, the maximum dimensions ofthe first fiberboard 450 are three feet wide by eight feet high. Theheight of the vertical splice 452 is the same as the height of the mainsheet 454. Preferably, the dimensions of side stiles 416 and 418 areone-and-one-quarter inches by one-and-one-half inches. Preferably, thedimensions of the bottom rail 412 and the top rail 414 areone-and-one-quarter inches by one-and-one-half inches bythirty-three-and-seven-eighths inches.

The thickness of the first fiberboard 450 shown is nine-sixteenths of aninch. Alternatively, the thickness can be any other suitable thickness.The two major surfaces of the first fiberboard 450 include afront-facing surface 451 and a rear-facing surface (not shown). Thefront-facing surface 451 and the rear-facing surface of the firstfiberboard 450 are disposed on opposing sides of the first fiberboard450. Either the front-facing surface 451 or the rear-facing surface ofthe first fiberboard 450 can be disposed adjacent to a rear-facingsurface of a front face 440. According to the embodiment, thefront-facing surface 451 of the first fiberboard 450 is disposedadjacent to the rear-facing, surface of the front face 440. Thus, therear-facing surface of the first fiberboard 450 is disposed adjacent toone of the major surfaces of the porous layer 470.

Preferably, the porous layer 470 is formed by disposing a horizontalsplice 472 adjacent to a main sheet 474. Alternatively, the porous layer470 can be a single sheet. The horizontal splice 472 is disposedproximate the top rail 414. Alternatively, the horizontal splice 472 isdisposed proximate the bottom rail 412. The height of the horizontalsplice 472 can be any suitable dimension. For example, the height of thehorizontal splice 472 can be 16 inches. The height of both thehorizontal splice 472 and the main sheet 474 corresponds to the heightof the door 410. Thus, the maximum dimensions of the porous layer 470are three feet wide by eight feet high. The width of the horizontalsplice 472 is the same as the width of the main sheet 474. The thicknessof the porous layer 470 is three-eighths of an inch. Alternatively, thethickness can be any other suitable thickness.

The two major surfaces of the porous layer 470 include a front-facingsurface 471 and a rear-facing surface (not shown). The front-facingsurface 471 and the rear-facing surface of the porous layer 470 aredisposed on opposing sides of the porous layer 470. Either thefront-facing surface 471 or the rear-facing surface of the porous layer470 can be disposed adjacent to the rear-facing surface of the firstfiberboard 450. According to this embodiment, the front-facing surface471 of the porous layer 470 is disposed adjacent to the first fiberboard450. Thus, the rear-facing surface of the porous layer 470 is disposedadjacent to one of the major surfaces of the second fiberboard 480.

The second fiberboard 480 is formed by disposing a vertical splice 482adjacent to a main sheet 484. Alternatively, the second fiberboard 480can be a single sheet. The vertical splice 482 is disposed proximate theside stile 416. Alternatively, the vertical splice 482 can be disposedproximate the side stile 414. The width of the vertical splice 482 canbe any suitable dimension. For example, the width of the vertical splice482 can be six inches. Preferably, the width of both the vertical splice482 and the main sheet 484 corresponds to the width of the door 410.Thus, the maximum dimensions of the second fiberboard 480 are three feetwide by eight three high. The height of the vertical splice 482 is thesame as the height of the main sheet 484.

The thickness of the second fiberboard 480 is preferably nine-sixteenthsof an inch. Alternatively, the thickness can be any other suitablethickness. The two major surfaces of the second fiberboard 480 include afront-facing surface 481 and a rear-facing surface (not shown). Thefront-facing surface 481 and the rear-facing surface of the secondfiberboard 480 are disposed on opposing sides of the second fiberboard480. Either the front-facing surface 481 or the rear facing surface ofthe second fiberboard 480 can be disposed adjacent to the rear-facingsurface of the porous layer 470. According to this embodiment, thefront-facing surface 481 of the second fiberboard 480 is disposedadjacent to the rear-facing surface of the porous layer 470. Thus, therear-facing surface of the second fiberboard 480 is disposed adjacent toone of the major surfaces of the rear face 490.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations, and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined by the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

1-18. (canceled)
 19. A method of making a door comprising: providing acore comprising a porous layer having two opposing major surfaces and atleast three fire-retardant layers each comprising a fiberboard; andcoupling together the porous layer and the at least three fire-retardantlayers in an unbalanced construction, wherein a number of the at leastthree fire-retardant layers disposed on one of the two opposing majorsurfaces of the porous layer is greater than a number of the at leastthree fire-retardant layers disposed on another one of the two opposingmajor surfaces of the porous layer. 20-21. (canceled)
 22. The method ofmaking the door according to claim 19, further comprising: coupling afirst exterior layer to one surface of the core; and coupling a secondexterior layer to another surface of the core, wherein a door blank isformed.
 23. The method of making the door according to claim 22, furthercomprising applying a uniform pressure to the door blank for a period oftime.
 24. The method of making the door according to claim 23, whereinthe uniform pressure is in a range between about 80 and about 110 poundsper square inch and the period of time is about 30 minutes. 25-40.(canceled)
 41. The method of making the door according to claim 22,further comprising machining a grooved first pattern having a firstdepth on the first exterior layer.
 42. The method of making the dooraccording to claim 41, wherein the first depth penetrates a thickness ofthe first exterior layer and a portion of a thickness of one of the atleast three fire retardant layers.
 43. The method of making the dooraccording to claim 42, further comprising machining a grooved secondpattern having a second depth on the second exterior layer, wherein thesecond depth penetrates a thickness of the second exterior layer and aportion of a thickness of another one of the at least three fireretardant layers.
 44. The method of making the door according to claim43, wherein the first and second depths are about the same.
 45. Themethod of making the door according to claim 19, wherein a density ofthe porous layer is at least one pound per cubic foot.
 46. The method ofmaking the door according to claim 19, wherein the porous layercomprises a thermoplastic polymer.
 47. The method of making the dooraccording to claim 19, wherein the porous layer comprises afire-retardant material.
 48. The method of making the door according toclaim 19, wherein a thickness of each of the at least threefire-retardant layers is about the same.
 49. The method of making thedoor according to claim 48, wherein a thickness of the porous layer isabout the same as the thickness of each of the at least threefire-retardant layers.
 50. The method of making the door according toclaim 19, wherein the fiberboard comprises a medium-density fiberboardcomprising a density of at least 42 pounds per cubic foot.